Molecular Dynamics Simulations of Nanoindentation of Gold Substrate in (100), (110), and (111) Directions

Nanoindentation is one of the various methods applied to measure the mechanical properties of small samples. In this study, three-dimensional molecular dynamics simulation was used to investigate the behavior of thin gold films during nanoindentation under different indentation depths and Au lattice directions. The indenter employed in the simulation is a diamond tip with a spherical shape. The substrate was made of single crystal Au. The simulations were repeated for Au (100), (110), and (111). The load displacement response of the gold film was examined during a full indentation cycle, i.e. loading and unloading periods. Young’s modulus for the gold was obtained from the unloading curve’s slope and compared to those of experiments. It was observed that increasing the indentation depth results in a decrease in Young’s modulus. In addition, for the lowest indentation depth, 4 Å, the Young’s modulus in (111) was found to be the largest among other lattice directions, and then there were the modulus corresponding to (100) and (110), respectively. However for larger depths, the trend was different and discussed in the present study. Comparison to the experimental values yielded that the moduli from the simulations were higher than the experiments. We further discussed the reasons attributable to this difference.